Semi-conductive device



April 1953 w. A. J. M. ZWIJSEN 3,085,180

SEMI-CONDUCTIVE DEVICE Filed June 10, 1955 INVENTOR WILHELMUS ANTONIUS JOSEPH MARIE ZWIJSEN AGEN United States Patent 3,085,180 SEMI-CGNDUCTIVE DEVICE Wilheirnus Antonius Joseph Marie Zwijsen, Eindhoven, Netherlands, assignor, by mesne assignments, to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed June 10, 1955, Ser. No. 514,619 Claims priority, application Netherlands June 30, 1954 Claims. (Cl. 317-234) This invention relates to semi-conductive devices comprising a semi-conductive body and at least one electrode in rectifying contact therewith, and in particular to such devices in combination with heat dissipating means.

One such combination shows a transistor or crystal diode arranged in a vessel filled in part with a cooling liquid. Such a system, which is placed in paraffin, has been described in Electronics 26, 202, October 1953. A similar combination is known in which the semi-conductive device is immersed in a liquid having a boiling point just below the highest temperature which the device, in this case a rectifier, could attain. The purpose of this was to produce boiling of the liquid as soon as, but not before, the rectifier approached a dangerous temperature region. Liquids having a boiling point of bet-ween 65 and 70 C. were recommended for selenium rectifiers.

The two known systems described above have in common the feature that the liquid does not boil in normal operation. However, the present invention is based on the realization that it is advantageous for the heat produced in the electrode system or semi-conductive device during normal operation to be dissipated by means of a boiling liquid. The invention is also based on the realization that the mere selection of a liquid having a boiling point below that in the known systems is not sufiicient, since the manner in which the liquid boils also influences the speed with which heat may be dissipated. For exwhich a saturated vapor exists, the liquid exhibiting the characteristic that its reduced pressure at the lowest and highest operating temperatures of the semi-conductive devices is at least 0.01 and at most 0.9, respectively. If the liquid is a mixture, this mixture is required to satisfy the abovementioned conditions. The term reduced pressure when used herein means the ratio of the pressure of the saturated vapor of the liquid divided by its critical pressure.

The term lowest operating temperature is commonly understood to mean room temperature (3.). If for certain applications the semi-conductive device is to be operated at very low temperatures, it is necessary to ensure that the liquid reaches the prescribed reduced pressure at these low temperatures.

The highest or maximum operating temperature-at least in the semi-conductive devices used nowadays-is substantially dependent upon the kind of semi-conductive material and more particularly upon the distance between the valence band and the conduction band. The maximum operating temperature is about 60 C. for devices containing germanium; it is much higher in the case of silicon. It will be evident that the highest operating temperature may also be limited by other factors, for example, by the fusing point of the metal or the alloy of which 3,085,180 Patented Apr. 9, 1963 the electrodes are made. In general, the operating range of semi-conductive devices is fixed by the manufacturer thereof.

The invention is particularly suitable for cooling very small electrode systems such as high-frequency transistors and diodes in which the heat-dissipating surface of the system is very small, for example, smaller than 1 0111. or even smaller than 10 square millimetres. However, this does not imply that if the invention were applied to systems of larger size, the dissipation of heat would not also take place much more efiiciently than if the conventional liquids having a comparatively high boiling point were used.

The invention will now be described with reference to the accompanying drawing, of which the sole FIGURE shows a cross-sectional view of a transistor in a glass vessel on an enlarged scale.

In the drawing, the vessel used is a small glass tube having a comparatively thick wall 1 and in the lower end of which three conductors Z are sealed in a manner similar to incandescent lamps. The upper end 3 of the tube is closed by sealing. One of the conductors 2 carries a small germanium body 4 and the other two conductors are connected to the emitter and collector electrodes of the transistor made with that body 4. The diameter of these electrodes are 250p. and 400m, respectively. The heat produced in the electrode system 4 during operation must be dissipated to the liquid substantially by the emitter and the collector, the cooling surface thus being approximately 0.2 mmP. The cooling liquid, indicated by 5, is, for example, propane. Above the liquid in the space 6 is a saturated vapor.

The transistor thus described may be loaded so heavily that the dissipated power is 300 milliwatts. Such a transistor is suitable for use in a small transmitter. For comparison purposes, it is noted that the filament of a small incandescent lamp of 6 volts, 0.05 amp. dissipates the same power, whereas the surface enveloping the filament is larger. Consequently, if during boiling of the cooling liquid surrounding the transistor the so-called spheroidal state would arise, the semi-conductive device would be immediately destroyed.

In the construction of the invention, it results that the internal pressure within the vessel in most cases is several atmospheres at room temperature, and may be several tens of atmospheres at the maximum operating temperature of the device. In this respect, the liquids used in accordance with the invention are distinguished from those hitherto used, which start to boil only at the maximum operating temperature, that is to say, far above room temperature. Further, although a glass tube is resistant to very high pressures due to the fact that it may be of very small size for many types of electrode system-s, it is preferable from the viewpoint of safety that the vessel 1 is constituted of metal.

In selecting a cooling liquid, it is also necessary to ensure that the electrical properties of the system are not endangered thereby. As a rule, polar liquids should not be used.

It has been found after extensive experimentation that the risk of an unstable boiling situation occurring is, to a first approximation, proportional to the heat produced in the electrode system and inversely proportional to the surface area of the system which is in contact with the liquid and to the critical pressure of the liquid. It is thus preferable to utilize a liquid having a high criitcal pressure. In fact, the higher this pressure, the more heat may be dissipated safely. However, it is necessary to take care that the vapor pressure at the lowest operating temperature is at least 0.01 times the critical pressure.

The table following hereinafter shows the boiling point j B.P., critical temperature T;;, the critical pressure P in atmospheres, and the reduced pressure r at different temperatures for several cooling liquids.

between 0.01 and 0.9 in said temperature range, said liquid having a boiling point substantially below +60 C. whereby said liquid is maintained in a boiling condi- B.P.. TK PK 1r 11- 7r 1r (C.) (C.) (at-) 10 C. 20 C 60 C 150 C 1. C3HB.p1'0pane 42 95.6 43

4. C N ,cyanogen 20 128 59 5. Ctl li isobutane. -10 13 1 3 6. G llian-butane --0.6 153 3G 7. 051112. pcntauo 36 197.2 33

fluorocthane) 47 214 33. 7

The formula and the chemical names are given for each 15 liquid, except for the numbers 2 and 3, which relate to compounds containing fluorine and which are known under the trademark Freon followed by the character F and a number. Example 8 also is a Freon type liquid, which in general are highly fluorinated liquid organic compounds.

As will appear from the table, all the liquids specified therein may be used at operating temperatures in the range between 20 C. and 60 C. At the latter temperature, the reduced pressure 1r is still far below the upper limit of 0.9.

If the application requires the electrode system to be at a low temperature such as l0 C., only the liquids numbered 1 to 3 and 6 may be used, since the reduced pressure of the other liquids is too low at this temperature. On the other hand, it the electrode system is to be operated at a high temperature, for example, +150 C., only the liquids numbered 7 and 8 of the examples can be used, since the critical temperature of the other ones is lower than 150 C. or, in the case of n-butane, so little higher than 150 that the reduced pressure is higher than 0.9.

it will be evident that many other examples of suitable liquids for certain temperature ranges could have been provided in the table, but this was not done because those skilled in the art may readily ascertain, with the aid of known data, whether a particular liquid satisfies the conditions of the invention.

vWhile l have described my invention in connection with specific embodiments and applications, other modifications thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. An electrode system comprising a vessel, a cooling 0 liquid partially filling said vessel to produce a space above the liquid containing saturated vapor, and a semi-conductive device adapted to operate in a temperature range between minimum and maximum values and mounted within the liquid, the reduced pressure of the liquid at the lowest and highest temperatures in the temperature range of 20 to C. being at least 0.01 and at most 0.9, respectively, said liquid having a boiling point substantially below said maximum operating temperature.

2. An electrode system as claimed -in claim 1, wherein 60 the contact surface between the device and the liquid is smaller than 1 cm.

3. An electrode system as claimed in claim 1, in which the contact surface between the device and liquid is smaller than 10 mmfi.

4. An electrode system comprising a closed vessel, a liquid within and only partially filling said vessel to produce a space containing saturated vapor of the liquid, and a semi-conductive device adapted to operate over a temperature range of 10 C. to I+60 C. and immersed 7 within said liquid, said liquid having a reduced pressure tion throughout perature range.

5. An electrode system comprising a closed vessel, a liquid within and only partially filling said vessel to produce a space containing saturated vapor, and a semiconductive device adapted to operate over a temperature range of+20 C. to C. and immersed within said liquid, said liquid having a reduced pressure between 0.01 and 0.9 in said temperature range, said liquid having a boiling point substantially below +60 C. whereby said liquid is maintained in a boiling condition throughout substantially the entire said temperature range.

6. An electrode system comprising a closed vessel, an organic liquid within and only partially filling said vessel to produce a space containing saturated vapor, and a semi-conductive device having a heat dissipating surface less than one square centimeter and adapted to operate over a temperature range of +20 C. to .+60 C. and completely immersed within said liquid, said liquid having a reduced pressure between 0.01 and 0.9 within said temperature range, said liquid having a boiling point at which it is maintained in a boiling condition throughout substantially the entire temperature range.

7. An electrode system as set forth in claim 6 wherein the liquid is propane.

8. An electrode system as set forth in claim 6 wherein the liquid is butane.

9. In combination, a hermetically sealed container, 21 semi-conductor device disposed in said container, said semi-conductor device having a definite maximum operating temperature limit, and a vaporizable liquid having a boiling point not greater than the maximum operating temperature of said semi-conductor device partially filling the container and covering the semi-conductor device for maintaining the temperature of said semi-conductor device within the maximum operating temperature limit of said semi-conductor device, said vaporizable material comprising a highly fiuorinated liquid organic compound.

10. In combination, a hermetically sealed container, :1 germanium device disposed in said container, said germanium device having a definite maximum operating temperature limit, and a vaporizable liquid having a boiling point not greater than the maximum operating temperature limit of said germanium device partially filling the container and covering said germanium device for maintaining the temperature of said germanium device within the maximum operating temperature limit of said germanium device, said vaporizable material comprising trichlorotrifluoroethane.

substantially the entire said tem- References Cited in the file of this patent UNITED STATES PATENTS 2,288,341 Addink June 30, 1942 2,520,691 Otis Aug. 29, 1950 FOREIGN PATENTS 51,318 Netherlands Oct. 15, 1941 

1. AN ELECTRODE SYSTEM COMPRISING A VESSEL, A COOLING LIQUID PARTIALLY FILLING SAID VESSEL TO PRODUCE A SPACE ABOVE THE LIQUID CONTAINING SATURATED VAPOR, AND A SEMI-CONDUCTIVE DEVICE ADAPTED TO OPERATE IN A TEMPERATURE RANGE BETWEEN MINIMUM AND MAXIMUM VALUES AND MOUNTED WITHIN THE LIQUID, THE REDUCED PRESSURE OF THE LIQUID AT THE LOWEST AND HIGHEST TEMPERATURES IN THE TEMPERATURE RANGE OF 20* TO 60* C. BEING AT LEAST 0.01 AND AT MOST 0.9, RESPECTIVELY, SAID LIQUID HAVING A BOILING POINT SUBSTANTIALLY BELOW SAID MAXIMUM OPERATING TEMPERATURE. 